The present invention relates to an information recording medium such as a rewritable optical disk or the like. The present invention also relates to an information recording apparatus and method for recording information on an information recording medium such as a rewritable optical disk or the like. Furthermore, the present invention relates to an information reproduction apparatus and method for reproducing information recorded on the rewritable information recording medium.
In recent years, rewritable optical disks on which data can be randomly recorded have been extensively studied and developed. Of such disks, a rewritable optical disk called a DVD-RAM having a diameter of 120 mm is known. The DVD-RAM has concentric zones. The DVD-RAM is controlled at different rotational speed in units of zones. That is, outer zones have lower rotational speeds. However, the rotational speed is controlled to be constant within a single zone. Such rotation control is called ZCLV.
On each zone, a zigzag spiral track is formed. This zigzag pattern is called a wobble. The spiral track is defined by a groove track and land track, and by tracing the spiral track, the groove and land tracks alternately appear every round. A plurality of sector fields are formed along the spiral track. One sector field is formed of a header field and recording field. The header field records address data by embossed pits. That is, the respective sector fields hold address data.
If one round of spiral track is counted as one track, the respective zones have the same number of tracks. Also, tracks in a given zone have the same number of sector fields. Furthermore, the difference between the numbers of sector fields per track in two neighboring zones (outer and inner peripheral zones) is 1. That is, the number of sector fields per track in an outer peripheral zone is larger by 1 than that of an inner peripheral zone. In this way, by setting the number of sector fields per track in an outer peripheral zone to be larger than that of an inner peripheral zone, the recording efficiency in the DVD-RAM is improved. Since the respective tracks in a single zone have the same number of sector fields, the header field positions in that zone can be linearly aligned in the radial direction of the disk.
On the DVD-RAM, data are recorded in units of ECC blocks appended with error correction codes. Each block consists of 16 sector data. One sector data is recorded in the recording field of one sector field. The data recording scheme in units of blocks is the same as that of a DVD-ROM as a read-only optical disk.
As described above, since the header field positions in a single zone are linearly aligned in the radial direction of the disk, each recording field is not influenced by embossed pits included in the header field. Since address data are assigned in advance in units of sector fields, an arbitrary address can be accessed without initializing a disk. Furthermore, since address data can be obtained from each sector field as needed, the seek time can be shortened, and data can be randomly written in the recording field of an arbitrary sector field.
However, when each sector field has address data, the storage capacity decreases accordingly. Also, buffer fields and the like are required in addition to those used to record target data, and the storage capacity decreases accordingly. The buffer fields include those used to cope with changes in sector field length caused by rotational variation and eccentricity of a disk upon recording/reproduction of data, and those used to cope with random shifts of recording positions when phase change recording is used.
For the reasons described above, the storage capacity of the DVD-RAM is about 10% smaller than that of the DVD-ROM. Furthermore, the disk is segmented into a plurality of zones from the inner periphery toward the outer periphery, and upon jumping from a given zone to another, the recording frequency changes largely. For this reason, when data such as video data are to be recorded in a large quantity, a long time is required to make the disk cope with a change in frequency. Such long time decreases the transfer rate and makes seamless recording difficult. Address data recorded as embossed pits is located between the land and track grooves, and is reproduced at the tail of a beam spot that tracks the land or groove. For this reason, high-precision embossed pit recording is required, and it is difficult to adjust an optical head to precisely reproduce embossed pits, resulting in an increase in cost.
A prevalently used CD-R or CD-RW does not adopt any scheme of assigning address data in units of sector fields. In the CD-R or CD-RW, address data is reflected as an FM signal in a wobble of a track. In a DVD-R, address data is recorded using land prepits which do not impose any influences upon reproduction by a DVD-ROM drive. In these disks, it is difficult to efficiently record data at arbitrary positions. Also, in these disks, a recording end process is required after data recording, and mostly dummy data are recorded over several hundred tracks. Such recording scheme is suitable for recording continuous data such as video data, but is not suitable for recording small fragments of data such as computer data.
As described above, when the conventional optical disk recording scheme adopts a format suitable for recording random data, such format results in recording efficiency drop or is not suitable for continuous recording. Conversely, when a format suitable for continuous recording is adopted, it is not suitable for recording random data.